Limited Reactants
- Usually one reactant gets used up first
- One reactant is completely consumed
- This determines how much product is produced
- "Guess" which reactant is limiting and check how much of the other is required
Examples:
What is the limiting reactant when 12.5 g of P4 reacts with 323 g of Cl2 to form Phosphorous trichloride?
First, come up with the balanced equation: P4 + 6Cl2 -----> 4 PCl3
12.5 g x 1 mol/124 g x 6 mol Cl2/ 1 mol P4 x 71 g/ 1 mol = 431 g of Cl2
Cl2 is the Limiting Reactant
Determine the theoretical yield of the previous reaction
323 g = theoretical yield
431 g = Actual yield
323 g x 1 mol Cl2/71 g x 4 PCl3/6Cl2 x 137.4/1 PCl3 = 417 g
In the formation of Water, 50 g of Oxygen gas reacts with 20 g of Hydrogen gas. Determine the LR,the theoretical yield and how much excess reactant will be left.
2H2 + 2O2 -----> H2O
50 g x 1 mol.32 g x 2 mol H2/1 mol O2 x 2 g/ 1 mol = 6.25 g H2
LR is O2
Theoretical: 50 g x 1 mol/32 x 2 mol H2O/1 mol O2 x 18.0/ 1 mol H2O = 56 g (theoretical yield)
20 g - 6.25 g H2 = 14 g (excess)
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Here's a site with a few notes and an example on the limiting reactant:
Here's a video on identifying the limiting reactant:
